The invention relates to a thermal bonding method and an apparatus for the method. Particularly, it relates to a thermal bonding method and an apparatus for bonding two members laminated with an adhesive interposed therebetween by heating and pressing, which enable uniform and efficient heating and continuously bonding plural sets of members, and are therefore excellent in bonding accuracy and cost.
Conventionally, bonding two members with an adhesive has been performed by a thermal bonding method wherein two members are laminated with an adhesive interposed therebetween into one body which is then pressed with a jig and passed through a tunnel-like heating furnace while being pressing continuously to thermally melt or thermally cure the adhesive in the heating furnace.
For example, in production of brake shoe assemblies for drum brakes, bonding brake shoe bodies and friction linings with adhesives has been performed by coating a brake shoe body and a friction lining with a thermosetting adhesive, drying, setting them in a pressing jig, and then heating in a thermally curing furnace with hot blast to cure the thermosetting adhesive.
However, thermally curing thermosetting adhesives with hot blast involves the problems that quick curing is difficult due to the low heat transfer, and that it cannot heat the parts coated with adhesives efficiently, because other parts, such as jigs, transfer instruments and the walls of the furnace, are also inevitably heated. To solve such problems and achieve downsizing of equipment and quicker heating, the use of high-frequency induction heating is proposed in Japanese Patent Application Non-examined Publication No. 61-153026. The method enables quicker heating, but is poor in heating efficiency because it is an indirect heating using an eddy current. Another shortcoming is that the method needs coils and equipment of complicated structures to uniformly heat brake shoe bodies of complicated shapes.
In Japanese Patent Application Non-examined Publication No. 9-48953 disclosed is another bonding method wherein while pressure is being applied, one of the members to be bonded is placed in contact with a heated holder to heat it by heat conduction from the holder. In this method, bonding with heat and pressure is performed quickly and efficiently. However, in cases where the surface of the member to be bonded by the method is coated with a coating, such as a primer for coating the surfaces of brake shoes, there arises problems in that the coating transfers to the holder during thermal curing and is peeled off from the product.
In Japanese Patent Application Non-examined Publication No. 9-144793 disclosed is another method of bonding a brake shoe body with a friction lining by laminating them with an adhesive interposed therebetween and then bonding with heat and pressure, wherein the heat for bonding is generated by the brake shoe body itself by electrically charging the brake shoe body through electrodes pressed to both ends of the brake shoe body. However, to heat the brake shoe uniformly by this method, complicated control is required, for example, cooling the electrodes and the parts not bearing the friction lining, or adjusting the pressure to the electrodes to prevent partial overheat due to contact resistance. Further, adhesives generate gas during cure with heat, and, in this method wherein only the electrically charged brake shoe body generates heat, the gas is cooled and condensed, adhering to the electrodes or jigs. In addition, the method efficiently reduces the heating time, but necessitates preparation of many apparatuses since the complicated heating system permits only one laminate to be bonded by one apparatus.
The object of the invention is to provide a thermal bonding method and an apparatus for the method which enable quick and thermally efficient bonding with heat and pressure using adhesive, such as bonding shoe rims of brake shoe bodies with friction linings, prevent peeling of surface coating, and enable continuous production of plural bonding products using simple instrument.
After study to solve the above-described problems, the inventors have accomplished the invention based on the finding that the problems can be solved by using radiant heat as the heat for bonding with heat and pressure.
Accordingly, the invention provides a thermal bonding method for bonding at least two members to each other with an adhesive by pressing and heating a laminate formed by laminating the members on each other with the adhesive interposed therebetween, comprising placing at least one member of the laminate close to a heated radiation heater and pressing the laminate in a radiant heat-applied state.
The method of the invention does not need adjustment of pressure nor partial cooling for temperature control, and the simplified heating procedure reduces the production cost. It also prevents peeling of the coating on laminates, because the laminate is not heated by heat conduction but by radiant heat requiring no contact with heaters. Further, since radiant heat also gives a high temperature atmosphere, the gas generating from the adhesive on curing does not condense to adhere to the apparatus. In addition, since the method of the invention is feasible with apparatuses of simple structures, apparatuses for simultaneous bonding of plural laminates can be constructed easily, thereby improving the production efficiency.
The invention also provides an apparatus for bonding at least two members to each other with an adhesive by pressing and heating a laminate comprising the two members and the adhesive interposed between the two members, which apparatus comprises a radiation heater, a supporting member for supporting the laminate with at least one member placed close to the radiation heater, and a pressing unit adapted to approach, contact and press the laminate supported on the supporting member and then move away from the laminate to stop applying a pressure to the laminate.